On 8/30/12 2:45 AM, "Andy Seaborne" <[email protected]> wrote:
>On 30/08/12 00:51, Rob Vesse wrote: >> Is there a particular class responsible for this renaming? > >The constants are in ARQConstants. > >The rename engine is in com.hp.hpl.jena.sparql.engine.Rename > >> Our developers would like to know exactly what forms Jena will use for >> variable names in the generated algebra as they've seen some other >>strange >> ones like ?*x as well as the ?/x > >IIRC ?*gNNN get allocated for some quad conversion. Can't remember what >exactly (non-simplified property paths in GRAPHs?) > >Is there a specific reason? (This is internal stuff that the systems >may change without notice.) A decision was made at some point in time to communicate queries internally within our system using the Jena algebra representation, then people complain every time they see something from Jena they hadn't seen before or expected (like the OpDisjunction I also asked about). > >If the execution strategy is not the constant-memory one the released >OpExecutor uses (and TDB[released]), then renaming isn't necessary as it >"just happens" as a result of bottom up evaluation. Converting to >global variables has some convenience though, such as debugging and not >needing to do internal projection. I'm not sure if we could do away with renaming and as you said it does have some advantages. Rob > > Andy > >> >> Rob >> >> On 8/29/12 10:24 AM, "Andy Seaborne" <[email protected]> wrote: >> >>> On 29/08/12 17:51, Rob Vesse wrote: >>>> Andy >>>> >>>> Just got a question from one of our devs about algebra ARQ is >>>> generating. The original query is sq-08.rq from the subquery tests of >>>> the 1.1 test suite, the following is the fragment of the algebra he >>>>was >>>> asking about: >>>> >>>> (extend ((?max ?/.0)) >>>> (group () ((?/.0 (max ?/y))) >>>> (quadpattern (quad <urn:x-arq:DefaultGraphNode> ?/x >>>> <http://www.example.org/schema#p> ?/y) >>>> >>>> Under what circumstances will ARQ insert slashes into variable names? >>> >>> When it needs to rename them to make then different from another use of >>> the same name in a different scope. It renames all variables that do >>> not show in the projection of subqueries if it detemines any renaming >>>is >>> needed. >>> >>> The GROUP BY isn't the trigger: this query is simpler and uses >>>renaming: >>> >>> PREFIX : <http://example/> >>> SELECT * >>> { >>> { SELECT ?x { ?x :p ?y } } >>> ?y :q ?r >>> } >>> >>> There are two separate uses of ?y in that query. >>> >>> { SELECT ?x { ?x :p ?y } } >>> >>> does not expose ?y so the use of ?y there is independent of the >>> " ?y :q ?r". >>> >>> If ARQ determines some renaming is necessary, it systematically renames >>> everything hidden by project scoping - it renames to only leave >>> variables that exposed. Hence the ?/.0 from the group aggregate. >>> >>> Andy >>> >>>> >>>> Thanks, >>>> >>>> Rob >>>> >>> >> >
